This invention relates to the field of antennas. More particularly, this invention relates to the method of electrically steering the radiated beam from the antenna array both for broadcast and receive antennae.
In an ever more competitive environment it is desirable to manufacture an antenna with the ability to adjust the orientation of the radiated beam. Due to continued cost constraints it is desirable to produce antenna of the most simple design and greatest ease of manufacture. By the electrical steering of the radiated beam the antenna structure can remain fixed and not require physical reorientation. A fixed antenna is desirable as it is more simple to adjust the antenna by a central actuator for the reorientation of the radiated beam. A fixed antenna also lends itself to the remote operation of the central actuator so as to remove the need to be physically present for the reorientation of the antenna radiated beam.
Several approaches may be used to down-tilt the radiation pattern from an antenna. One involves actually tilting an entire antenna, but this method is too rigid an approach and is also costly. Another approach electrically down-tilts the pattern by adjusting the relative phases of the radiation associated with each of several elements of a multi-element antenna. Another electrical down-tilt method is a capacitive coupling method, in which an adjustable capacitance is placed in series with the transmission line feeding each element of the antenna array, thus causing the desired phase shifts. Another approach is to use different lengths of transmission lines for feeding the different elements; which produces a permanent electrical down-tilt. Yet another approach is to provide continuously adjustable down-tilting by mechanically varying the amount of dielectric material included in the transmission line, usually using a rack and pinion gear assembly.
Producing a fixed electrical phase shift, however, is too rigid an approach for many applications. A fixed electrical phase shift solution cannot be altered to fit ratio. Of the state-of-the art continuously variable electrical phase-shifting methods, the capacitive coupling method produces inter-modulation products, and is generally only good for omni-directional antenna patterns. Therefore, existing methods of providing continuous phase shifting, for example using a rack and pinion assembly, are mechanically complex, and so are often unreliable and expensive. The complexity in these methods stems from translating rotational to linear motion in moving dielectric into or out of the transmission line. It is generally known in the art that a receive antenna responds, and is directly related, to a radiation pattern broadcast by the antenna. Thus, the methods associated with down-tilting a broadcast antenna are applicable to adjusting a receive antenna to improve its reception in a particular direction.
The present invention is an antenna feed system which includes a cooperative phase shift coupling mechanism, antenna body housing and transmission line elbows, which allow for the continuously variable phase shift to the antenna array that electrically reorients the radiation pattern of the radiated beam. The present invention overcomes many of the shortcomings of prior art. Instead of loading the transmission line with dielectric material to slow the wave passing through the section, the present invention simply adjust the length of the line progressively to each of the elements in the array. Without the introduction of dielectric, the present invention is not limited to the associated mismatch and phase shift adjustment limits of the prior art. Though prior art is referenced, the present invention achieves similar results, is an entirely different method than those that use dielectric loading.
An antenna feed system which includes a cooperative phase shift coupling mechanism, antenna body housing and transmission line elbows according to the present invention is capable of continuously varying the orientation of the radiated beam of the radiation pattern associated with an antenna, the radiation pattern comprising an RF signal, the antenna having a plurality of elements and having an element terminal for each element and further having a feed system for communicating the RF signal between each element terminal and a common feed terminal. An antenna feed system according to the present invention includes a phase shift coupling mechanism which is used to distribute RF energy from the two ends of a branch of floating center conductor, which creates a transmission line when placed in the center of one of the many cavities formed in an extruded or other wise formed antenna body housing, to the center of the adjacent and continuing center conductor centrally located inside the adjacent and continuing cavity and continuing RF path, by means of quarter wave length coupling or other odd multiple of quarter wave or other coupling probe, which is placed in the center along the axis of the extruded or otherwise formed center conductor having a shape with an opening on a side parallel to the axis so that the center area of the shape is able to be reached and allow space for a rod or probe of some design, not actually making contact but of such length or shape as the electrical equivalent at the operating frequencies is such that the length of open circuited line inside of the continuing center conductor behaves as if the line is shorted or actually making contact at the point of entrance into the center conductor or another point. It is this electrically equivalent connection by means of the phase coupling device which allows the adjustment of the length of the RF path from the end of each branch lines to the center of, or above center of or below center of the adjacent and continuing RF line so that the path length from each of the individual ends of branches of the previous adjacent line to each of the two ends of branches or two antenna terminals at the ends of the center coupled or about center coupled continuing line is made adjustable in length when comparing the RF path length from the previous end branch to the continuing end branch or antenna terminal located above the coupling point to the other end branch or antenna terminal located below the same coupling point.
This process continues from each adjacent line in the corporate feed system until antenna terminals are connected or are in communication with the central feed point. As the central feed point will now be moving in cooperation with the floating lines so as to distribute the RF energy to each of the elements in a progressive or approximately progressive manner, a means is necessary to connect this moving point to a stationary position. This is accomplished through a series of transmission line elbows.
These elbows include a common ground plane and a suspended center conductor forming a transmission line by location above the ground plane. Each arm of the elbow unit couples energy to the next arm of the elbow unit by means of a quarter wave or odd multiple of quarter wave length or other coupling design tubular or similarly shaped conductors each of which are attached receptively to the previous and continuing arms placed in coaxial or similarly effective relationship, one inside or about the other, but not in physical contact so that they form an open circuited transmission line at the operating frequencies of the antenna one quarter wave or odd multiple thereof or other design or length such that equivalent electrical contact is made between the adjacent and continuing arms in the RF path, perpendicular to the arms away from the contact point or in other relationship to allow their relative movements.
The arms due to their shape at the contact intersection, and relative positions of the contact tubes are allowed to move axially about the center axis of each of the contact tubes thus enabling the dynamic RF connection between the floating feed line to the antenna and to the stationary input connector.